Mitogen-activated protein kinase (MAPK) signaling cascades couple diverse extracellular and intracellular queues to appropriate cellular stress responses, including cell growth, differentiation, inflammation, and apoptosis (Kumar, S., Boehm, J., and Lee., J. C. (2003) Nat. Rev. Drug Dis. 2:717-726; Pimienta, G., and Pascual, J. (2007) Cell Cycle, 6: 2826-2632). MAPKs exist in three groups, MAP3Ks, MAP2Ks, and MAPKs, which are sequentially activated. MAPK3s directly respond to environmental signals and phosphorylate MAP2Ks, which in turn phosphorylate specific MAPKs. MAPKs then mediated the appropriate cellular response by phosphorylating cellular substrates, including transcription factors that regulate gene expression.
Apoptosis signal-regulating kinase 1 (ASK1) is a member of the mitogen-activated protein kinase kinase kinase (“MAP3K”) family that activates the c-Jun N-terminal protein kinase (“JNK”) and p38 MAP kinase (Ichijo, H., Nishida, E., Irie, K., Dijke, P. T., Saitoh, M., Moriguchi, T., Matsumoto, K., Miyazono, K., and Gotoh, Y. (1997) Science, 275, 90-94). ASK1 is activated by a variety of stimuli including oxidative stress, reactive oxygen species (ROS), LPS, TNF-α, FasL, ER stress, and increased intracellular calcium concentrations (Hattori, K., Naguro, I., Runchel, C., and Ichijo, H. (2009) Cell Comm Signal. 7:1-10; Takeda, K., Noguchi, T., Naguro, I., and Ichijo, H. (2007) Annu. Rev. Pharmacol. Toxicol. 48: 1-8.27; Nagai, H., Noguchi, T., Takeda, K., and Ichijo, I. (2007) J. Biochem. Mol. Biol. 40:1-6). ASK1 undergoes activation via autophosphorylation at Thr838 in response to these signals and in turn phosphorylates MAP2Ks, such as MKK3/6 and MKK4/7, which then phosphorylate and activates p38 and JNK MAPKs, respectively. ASK2 is a related MAP3K that shares 45% sequence homology with ASK1 (Wang, X. S., Diener, K., Tan, T-H., and Yao, Z. (1998) Biochem. Biophys. Res. Commun. 253, 33-37. Although ASK2 tissue distribution is restricted, in some cell types ASK1 and ASK2 have been reported to interact and function together in a protein complex (Takeda, K., Shimozono, R., Noguchi, T., Umeda, T., Morimoto, Y., Naguro, I., Tobiume, K., Saitoh, M., Matsuzawa, A., and Ichijo, H. (2007) J. Biol. Chem. 282: 7522-7531; Iriyama, T., et al. (2009) Embo J. 28: 843-853) In non-stressed conditions, ASK1 is kept in an inactive state through binding to its repressor Thioredoxin (Trx) (Saitoh, M., Nishitoh, H., Fuji, M., Takeda, K., Tobiume, K., Sawada, Y., Kawabata, M., Miyazono, K., and Ichijo, H. (1998) Embo J. 17:2596-2606), and through association with AKT (Zhang, L., Chen, J. and Fu, H. (1999) Proc. Natl. Acad. Sci. U.S.A 96:8511-8515).
Phosphorylation of ASK1 protein can lead to apoptosis or other cellular responses depending on the cell type. ASK1 activation and signaling have been reported to play an important role in a broad range of diseases including neurodegenerative, cardiovascular, inflammatory, autoimmunity, and metabolic disorders. In addition, ASK1 has been implicated in mediating organ damage following ischemia and reperfusion of the heart, brain, and kidney (Watanabe et al. (2005) BBRC 333, 562-567; Zhang et al., (2003) Life Sci 74-37-43; Terada et al. (2007) BBRC 364: 1043-49). Emerging evidence suggests that ASK2, either alone or in a complex with ASK1, may play important roles in human diseases as well. Therefore, therapeutic agents that function as inhibitors of ASK1 and ASK2 signaling complexes have the potential to remedy or improve the lives of patients suffering from such conditions.
U.S. Publication No. 2007/0276050 describes methods for identifying ASK1 inhibitors useful for preventing and/or treating cardiovascular disease and methods for preventing and/or treating cardiovascular disease in an animal. The methods comprise administering to the animal an ASK1 inhibitor and, optionally, a hypertensive compound. U.S. Publication No. 2007/0167386 reports a drug for at least one of prevention and treatment of cardiac failure containing a compound that inhibits a functional expression of ASK1 protein in a cardiomyocyte, and a method for screening the drug. WO2009027283 discloses triazolopyridine compounds, methods for preparation thereof and methods for treating autoimmune disorders, inflammatory diseases, cardiovascular diseases and neurodegenerative diseases.